Saddlebum, you are correct in that if the Lee FC die touches your brass over the bullet you will have loose bullet problems.
However, I love the Lee FC dies. But you have to have them set up right.
The FC die should be large enough to only touch a round which would otherwise not fit in the chamber at all. In other words, about .004" under your chamber diameter (chamber diameter, NOT throat diameter). Assuming the FC die is the right size (large enough diameter), if it sizes the lead bullet at all, that round would not have chambered anyway.
The FC die can be opened up by chucking in a lathe and using a dremel with a cylindrical diamond bit. Open it up to .004" under chamber diameter. Then you are ready to get full use out of it, as you will see below.
In station #1 I use a decapping die. All it does is decap. It doesn't touch the brass otherwise.
In station #2 I have my sizing die set up to NECK SIZE ONLY. It is backed mostly out of the toolhead, so it only sizes as far down the brass as the bullet is deep. I want my neck size I.D. to be about .004 or so under my cast bullet diameter, for good tension. And my FC die is TOO LARGE to ever touch this portion of the cartridge when I crimp it.
In station #3, my belling (expansion) plug barely touches the inside of the brass, not really opening it up any. You can reduce the diameter of these in a drill press with silicone carbide or aluminum oxide paper.
In station #4, I seat the bullet.
In station #5, I have my Lee FC die (which also crimps). This FC die nowhere near touches the bullet and neck of the brass case near the neck portion, because it is opened up to about .004 under my chamber diameter. IF the body of the brass case (the bottom half) is too large to chamber, this FC die sizes it down. I am, in effect, neck sizing only with my regular sizing die, while sizing the rest of the case with the FC die. This makes for a more accurate round and a much better seal.
For example, in the .45 Colt, chambers in Rugers commonly run .483". Throats are usually (nowdays) around .452". If I am shooting a .452" bullet, the I.D. on the neck should be around .448" after neck sizing. After seating the bullet, neck I.D. is of course now .452" and neck O.D. (on brass with .011" thick walls) runs .474" -- unfortunately a full .009" smaller than the chambers. That's a lot of "slop" and not only leads to inaccuracy, but to gas blowby. Not a lot we can do about this with .452" bullets -- it is the fault of the manufacturers for keeping tolerances so sloppy.
I want to work my brass the least amount possible, and better accuracy to boot, so my FC die sizes the bottom portion of the brass .004" under the chamber measurements (.479"), which springs back a couple thousands to around .481" after pulled back out of the die. So the bottom of the brass, at least, has minimal slop -- only .002" clearance to be able to chamber the round. The front though has been worked a lot more, and will not center the bullet well unless the front driving band of the bullet enters partially into the throat. It's a compromise at best.
Veral Smith recommends going with vastly oversized bullets, matched to the CHAMBERS and not THROATS, to remedy this. In other words, with the above revolver you would load bullets sized to .459", which would make your neck O.D. (with brass walls being .011") .481". .002" is all you need if you keep the chambers clean. I haven't tried this, but he claims that the bullet would then be less apt to tip cockeyed upon beginning forward movement, and would be uniformly sized down as much as .010" in some cases by the time it made it through the bore.
Anyway, that is the right way to use the Lee FC die. Redding, I believe, just came out with a die with two carbide rings in the same die, with the same idea in mind. Only problem is, Saddlebum, just like you are thinking, revolver dimensions vary, and the carbide rings may have to be adjusted in I.D. It is easy on the Lee. But may be more difficult with two rings in the same die.
All said though, neck sizing works great in rifles, and also works great in revolvers!